1. Field of the Invention
This invention relates to an electronic device having a front cover and a capacitive proximity sensor, comprising: a first electrode and a second electrode, said first electrode having a large face; and detector means connected to the first electrode and the second electrode for detecting the capacitance of the first electrode relatively to the second electrode and for providing a control signal responsive to the capacitance.
2. Description of Related Art
Capacitive proximity sensors are used in various applications in electronic devices e.g. instead of a push button in a telephone handset. Thereby, a particular function can be activated by e.g. moving a hand in the vicinity of the electronic device.
Systems using capacitive proximity sensors typically measure the capacitance or change in capacitance of an electrode with respect to its environment. That is the electromagnetic field propagating from the electrodes is changed when an object is moved into the field. Thus, it is possible to detect an object which is moved relative to the electrode.
When a capacitive proximity sensor is used in smallsized-hand-held electronic equipment, especially mobile telephones, it is extremely important that the proximity sensor can be incorporated in such small-sized electronic equipment without requiring larger dimensions of the electronic equipment. Typically, it is a requirement that it shall be possible to have access to all functions of the electronic device via a front cover providing access to user interface means such as a display, a keypad, a loudspeaker, etc.
U.S. Pat. No. 5,337,353 discloses a capacitive proximity sensor for use, e.g., in a telephone handset to sense whether an object, e.g., a user, a table, or another object, is in the proximity of the telephone handset. The disclosed proximity sensors include a sensing electrode mounted in parallel to a guard electrode; the electrodes are separated by an insulating layer. The sensing electrode and the guard electrode are driven in unison by an RF signal. The proximity of an object to the sensor is detected by monitoring the RF current flowing through the sensing electrode by means of a bridge coupling.
Despite the fact that numerous embodiments are mentioned or disclosed, the disclosure comprises embodiments in which the electrodes are made as plane electrodes arranged parallel to each other only.
Thus in the prior art, when the proximity sensor is used in small-sized electronic equipment, the proximity sensor will take up a considerable area on the front cover. Alternatively, the electromagnetic field is diminished or disturbed by components such as a loudspeaker, a display, a keypad, etc., since such components typically comprise electrical conductive materials.
Consequently, the prior art involves the problem that the geometry of the electrodes does not have a spatial relationship or shape that allows them to fit into small-sized electronic equipment while providing a sufficient sensitivity of the proximity sensor.
Thus an object of this invention is to provide a proximity sensor with electrodes which are arranged to fit into small-sized electronic equipment while providing a sufficient sensitivity of the proximity sensor.
This is achieved when the device mentioned in the opening paragraph is characterized in that the large face of the first electrode is inclined relatively to the front cover.
Consequently, the electrodes for a capacitor are used to sense proximity. When an object moves closer to the device (i.e. the electrodes) the object will tend to concentrate the electrical flux density; and when the object moves farther away it will separate the lines of flux propagating from one of the electrodes towards the other electrode. The electrical properties of the object are thus used to modulate the capacitance of the capacitor used as a sensing element.